The present invention is related generally to systems and methods for determining the range between a transmitter of a radio frequency signal and a receiver of the signal, and more particularly to a system and method for determining such range in which the power consumed and the complexity of the system is reduced from conventional systems and methods and in which miniaturization is achievable.
Systems and methods for determining the range between a transmitter and receiver are well known. In some systems, an outbound ranging signal having a known power is transmitted from a base station to a receiver at an unknown distance. The receiver may respond to the ranging signal by transmitting a return signal upon receipt of the ranging signal. The range may be determined, for example, by computing the total transit time from transmission of the ranging signal to receipt of the return signal whereby the distance may be computed, or by measuring the power of the return signal whereby an estimate of distance may be computed using the inverse square law of signal strength over increasing distances.
There are two general methods of generating the return signal. The "bent pipe" approach includes a return signal that is an echo of the ranging signal transmitted on a different frequency than the ranging signal. While implementation is generally simple and miniaturization is feasible, the transmit power of the ranging signal can be high and the antenna diplexer for the second frequency can be difficult to build. Further, the range of such systems is generally limited when the signal-to-noise ratio of the ranging signal is negative because the signal-to-noise ratio of the return signal is much more negative. In addition, two frequency bands must be allocated when single band operation is more desirable.
In the "time of arrival" approach the actual time of arrival of the ranging signal is determined and a separate return signal is transmitted on the same frequency. These systems require less power than "bent pipe" systems and provide better performance. However, they are complex and more difficult to miniaturize.
Accordingly, it is an object of the present invention to provide a novel system and method for determining range between a transmitter and a receiver that obviates the problems of the prior art.
It is another object of the present invention to provide a novel system and method for determining range between a transmitter and a receiver in which a ranging signal includes a trigger for activating a reference chirp at a receiver that is compared to a chirp waveform in the ranging signal so that an accurately timed return signal can be generated.
It is yet another object of the present invention to provide a novel system and method for determining range between a transmitter and a receiver in which the timing of a grossly timed return signal is corrected before transmission.
It is still another object of the present invention to provide a novel system and method for determining range between a transmitter and a receiver in which a ranging signal includes a grossly timed trigger for activating a reference chirp that is used to provide a correction signal for correcting the timing of the return signal from the receiver so that the arrival time of the return signal may be used to determine range.
It is a further object of the present invention to provide a novel system and method for determining range between a transmitter and a receiver in which the return signal is compared to a further reference chirp at the transmitter, the timing of the further reference chirp being related to a predetermined range from the transmitter.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.